The overall goal of the proposed research is to understand how the vertebrate auditory system encodes time-varying biologically significant information in the presence of natural and artificially produced background noise. This will be accomplished by examining the temporal resolving ability of single auditory fibers and single cells in the central auditory system of anurans (frogs and toads) in the presence of narrowband, broadband, and natural background noise of various levels. Specifically, we shall address the following questions: (1) What are the absolute limits of phase-locking of single auditory neurons to sinusoidal stimuli and to what extent does phase-locking deteriorate in the presence of masking noise? (2) How is temporal coding affected by previous exposure to high-level noise (such as occurs in the animals' habitat)? (3) What are the temporal integration characteristics of the peripheral auditory system of anurans, are they affected by the level and character of the background noise, and do they reflect the characteristics of the animal's vocalizations? and finally, (4) How does the relative spatial orientation between signal and masker affect the temporal resolving ability of single cells? We believe these studies will provide much needed insight into the neural substrate underlying species-specific communication in adverse (noisy) environments, and that this work will serve as a model for the understanding fundamental problems of human speech perception in the presence of noise.